I have some audio files in FLAC format that have 5.1 channels. While I want these files for archival purpose, in day-to-day use I would prefer to have normal stereo AAC files, as they will play on a wider range of devices. Is there an easy way to convert a 5.1 channel FLAC to a stereo FLAC or stereo AAC? (I can already convert 5.1 FLAC to 5.1 AAC using XLD.) I'm using a Mac.